I had something considerably smaller in mind... 1m diameter or so.

Oh, it IS two years old.  I saw it on the recent posts list, so I didn't bother looking at the date.

The cuffs are as great as they sound, just putting in my input, but you can always buy the cuffs separately later and they're compatible with all models.

Thanks Martin for the updates, I thought Projump springs still sucked.

The link doesn't work for me.

OK, in the UK, Powerisers and Powerizers/Projumps are about equal value for the money.  Powerisers are somewhat better, particularly their new 2008 model with the stock snowboard bindings and cuffs, but the 20008 model is also more expensive.  That's what I have and I do like them very much.  In general, you really get what you pay for.  7leagues have very nice springs with a good character and you don't have to break them in, plus they are the quietest bock on the market, but they don't sell them with any special features.  No cuffs or pivoting footplates, although you can order snowboard bindings and upgraded kneebar bindings for a little extra.  7leagues are the most expensive bocks you'd be interested unless you're sitting on some dead relative's fortune. 

Powerskips are about a kilogram lighter than the other models, their springs are way better and last practically forever, and you can get them with pivoting footplates, but no cuffs.  Stiltwerks, inc. will sell you their Velocity Stilts, which are pretty much the same as Powerskips, but I think you can order them with whatever features you want and they're a bit lighter.

I'm in the USA, so you'll want to check for yourself, but here's a price list (in pounds)
Projump: 135-ish
Poweriser base model: not sure, but a little more than Projump
Poweriser 2008: 200-220
7leagues: 240-265
Powerskip: 700-800
Velocity Stilts: not sure, but probably 1000-1500

There's also a Powerizer Pro model I don't know much about, which has pivoting footplates but is otherwise fairly normal.  I'm guessing it would run about 170 pounds or so.  Worth looking into.  But don't get the Up-Wing/Redoxx/a few other names model.  Its frame is very different from normal bocks and looks extremely fragile.  There have only been a few failures, but its pivoting footplates are awkward and the cuffs are uncomfortable and unstable.  Not worth the money, whatever its price might come out to.

At 57kg, you'll want to get the 50-70kg springs.  If you go Powerizer, it's a little tricky because you're near the top of a category but not really close, but I think the m60s would get boring.  You'll probably be better off with m70s.  Rumor has it that Powerizer springs are a little soft.

As for getting in contact with do it on bocks, he's a member of this site.  Find his name on the member list and send him a personal message.

His legs are .ighter and longer than normal human legs.  It's hard to compare, but if you just look at his body shape compared to the guys he's racing against, there's a noticeable difference.  He's in great shape himself, but the guys he races against are rail-thin muscular machines.  If he gets the same times at a lower fitness level, I think he has an advantage.

Connect it to a backflip and you're golden!

Failing that, get a big inflatable yoga ball thingy and play football/soccer.  It's a lot easier for noobs, just thought it would be worth mentioning.

Oh no, it's Fugly Butkins!!

Sweet!  Next, do a backflip out of it and you will be super-special-awesome!!

Yeah...  If you're going to panic carrot buy, at least do it on bocks and hop out of the store.   

I have never heard a better idea in my life.

You bent the knee bars too?  While walking?  Impressive.  You don't need a whole new pair just for the knee bars, though.  You can get knee bars separately.  You could probably even just bend them back.

Oh yes, everything can be found several times over on this website.  About the springs, how much do you weigh?  Please use kilograms.

I'd also suggest making sure the bolts are all tight, especially at the joints.

Taping is a good idea, as the protection they come with is insufficient.  Scrapes and chips on springs eventually translate to breaks, so you'll want to do that.  Hockey tape works best.

I just think that kind of music is stupid and kids should make up their own minds, but that has nothing to do with me going or not.  I'm not going because it's too far.

No flip should be described as "not much".